Embodiments of the invention relate to methods and apparatus for trace gas analysis, in particular to optical gas analysis, and especially to detection of target species indicative of breakdown of insulating oil.
Gas analysis, where a sample may be analysed to determine the presence of one or more target species of gas, is useful in a range of applications.
One particular application is for monitoring of electrical components, such as transformers, in a high voltage electrical power generation or distribution system. Large scale electrical transformers may be used in various power generation or distribution systems. Various parts of the transformer need to be electrically insulated from other parts of the transformer and/or the surrounding environment and it is typical that at least part of the insulation is provided by an insulating oil. Insulating oil may for instance be provided within a housing to cool and insulate the transformer windings.
The insulating oil is chosen to have suitable properties for the expected normal operating conditions. However if an electrical fault develops this could result in abnormal operating conditions. For instance in the event of some electrical faults there may be significant localised heating of the insulating oil, above what may normally be expected, and/or an electrical discharge within the insulating oil. Such electrical faults can result in breakdown of the components of the insulating oil and generate decomposition gases dissolved within the oil.
Suitable insulating oils, such as mineral oil, generally contain long chain hydrocarbon molecules. Electrical faults may result in breakdown of the insulating oil into various different components, such as acetylene, ethane or ethylene for example. These decomposition components may be produced as gases dissolved in the insulating oil and may only be present if the insulating oil has been subjected to some abnormal operating condition. Detecting the presence of such decomposition gases thus provides useful information about the occurrence of electrical faults, which is useful as part of a monitoring system, for example for preventative maintenance.
Dissolved gas analysis is a known technique where a sample of the insulating oil may be tapped from the transformer and tested for the presence of any decomposition gases of interest. Detecting the presence of decomposition gases may be indicative of a fault and the type of decomposition gas, concentration and rate of change may provide information about the type and/or severity of the fault. Such dissolved gas analysis does typically however require oil to be removed from the transformer and often requires the oil to be sent to a dedicated testing laboratory.